1. Field of the Invention
The invention relates to a process for generating a signal dependent upon a liquid film on a surface, particularly a traffic surface. The invention furthermore relates to a device for generating a signal dependent upon a liquid film on a surface, particularly a traffic surface, and the use of such a process or device in an arrangement for determining the freezing point of the liquid.
2. Description of Background and Relevant Information
It is desirable to produce a signal that provides information on the thickness of a liquid film on traffic surfaces, which are understood as roads and rolling and starting/landing runways for aircraft, for example. Information can be obtained thereby on the danger of so-called hydroplaning (the floating of vehicle wheels on the portion of the water film impenetrable to the wheels), or a warning can be transmitted to users of the traffic surface. As is known, the danger of hydroplaning increases with the increasing thickness of the water film. Measuring the thickness of the water film as precisely as possible by way of the reflection of micro-waves is known from EP-A-0 432 360. But the process is an elaborate one. From U.S. Pat. No. 4,897,597, it is known that the water film thickness can be ascertained by measuring conductivity which, however, does not always lead to satisfactory results. DE-A-31 18 997, EP-A-0 045 106, and EP-A-362 173 disclose processes for determining the freezing point of a liquid but not for ascertaining the water film thickness. Patent Abstracts of Japan vol. 97, no. 8, Aug. 29, 1997 discloses the detection of an ice film thickness, where the thickness is detected by way of the installation distance of a temperature sensor from a heat exchanger line that is icing up.
The invention therefore provides for a simple and economical process for generating a signal that is dependent upon the liquid film. The invention is also directed to a corresponding device.
It has been shown that, by heating or cooling a portion of the liquid film and by measuring the increase or decrease in temperature with sufficient accuracy, a conclusion can be reached at least on the thickness range in which the liquid film thickness lies. As a rule, assigning the liquid film thickness to a thickness range or class suffices for the purposes of a hydroplaning warning. The process also permits the absolute thickness to be determined with a good degree of accuracy if a greater degree of effort is taken in evaluating the temperature curve.
The preferred device is one with a Peltier element for heating the liquid film. The reverse operation of the Peltier element also permits a cooling of the liquid film. Thus, the device can be additionally used to determine the freezing point of the liquid according to the process indicated in EP-A-0 045 106 or EP-A-0 362 173.
The invention provides for a process for generating a signal dependent upon a liquid film on a surface, particularly a traffic surface, characterized in that a portion of the liquid of the liquid film is heated or cooled by a heating arrangement or a cooling arrangement, the increase or decrease in the temperature of the heated or cooled portion is ascertained by a temperature measuring arrangement, and a value or value range for the thickness of the liquid film is assigned to the temperature increase or decrease by an evaluation device and is released as a signal. The process may be characterized in that an area is provided in the heating arrangement or cooling arrangement which is indented relative to the surface and in which area the liquid is heated. The process may be characterized in that the heating output or cooling output is kept constant during heating or cooling. The process may be characterized in that the initial temperature T0 of the liquid film is determined in each case before or at the beginning of heating or cooling. The process may be characterized in that a test on the presence of liquid is performed before the beginning of heating or cooling, and the heating arrangement or cooling arrangement is only activated when liquid is identified.
The invention also provide for a device for generating a signal dependent upon a liquid film on a surface, particularly a traffic surface, characterized in that a heating arrangement or a cooling arrangement by way of which a portion of the liquid film can be heated or cooled is provided, as well as a temperature measuring arrangement for determining the temperature of the liquid film that can be heated or cooled by the heating arrangement or cooling arrangement, and a control and evaluation device by way of which the heating arrangement or the cooling arrangement and the temperature measuring arrangement can be controlled and the signals of the temperature measuring arrangement can be evaluated, specifically in such a way that a thickness, or thickness range, of the liquid film is assigned to the measured temperature increase or decrease and is released as a signal. The device may be characterized in that said device includes mechanisms, particularly an electrode arrangement, for identifying the presence of liquid in the area of the heating arrangement. The device may be characterized in that the heating arrangement or cooling arrangement includes at least one Peltier element which is operated at a constant power. The device may be characterized in that said device exhibits a surface which can be aligned so as to be flush with the area, such that the liquid film uniformly covers the area and the surface of the device, and in the area of the heating arrangement or the cooling arrangement an indentation is provided in the surface.
The invention also provides for using the process in an arrangement for generating a signal indicating the freezing point of the liquid on the surface.
According to another aspect of the invention, there is provided a process for generating a signal dependent upon a liquid film on a surface, comprising subjecting a portion of the liquid film to a temperature change using one of a heating and a cooling arrangement, measuring a temperature change of the portion using a temperature measuring arrangement, assigning a value to the temperature change using an evaluation device which is related to a thickness of the liquid film, and producing a signal related to the value. The surface may be one of a road surface and a traffic surface. The assigning a value may comprise assigning a value range. The temperature change may comprise one of a temperature increase and a temperature decrease. The heating or cooling arrangement may comprise one of a heating and a cooling surface which is indented some distance from another surface of the arrangement. The liquid may be one of heated and cooled in the indented heating and cooling surface. The subjecting may comprise producing one of a constant heating output and a constant cooling output. One of the heating and the cooling arrangement may be adapted to produce one of a constant heating output and a constant cooling output.
The process may further comprise determining an initial temperature T0 of the liquid film. The determining may occur either before or at a beginning of the subjecting. The process may further comprise testing for the presence of the liquid film. The testing may be performed before the subjecting. The process may further comprise activating the heating or cooling arrangement upon identifying the presence of the liquid film.
The invention provides for a device for generating a signal dependent upon a liquid film on a surface comprising one of a heating arrangement and a cooling arrangement for subjecting a portion of the liquid film to a temperature change, a temperature measuring arrangement for determining the temperature of the liquid film, the temperature measurement arrangement being capable of producing a signal, and a control and evaluation device for controlling one of the heating arrangement and the cooling arrangement and the temperature measuring arrangement. The device may generate the signal when one of a predetermined thickness and a predetermined thickness range of the liquid film is ascertained. The surface may be one of a road surface and a traffic surface. The device may further comprise an electrode arrangement for identifying the presence of the liquid film in an area of the heating or cooling arrangement. The temperature measurement arrangement may comprise a measurement device which is connected to the electrode arrangement. The heating or cooling arrangement may comprise at least one Peltier element which is operated at a constant power. The heating or cooling arrangement may comprise one of a heating and a cooling surface which is indented some distance from an exterior surface of the arrangement. The liquid may be one of heated and cooled in the indented heating and cooling surface. The exterior surface may be adapted to be aligned with a road surface when the device is disposed in the road surface.
The invention also provides for a method for generating a signal dependent upon a liquid film on a surface with a device that includes one of a heating arrangement and a cooling arrangement for subjecting a portion of the liquid film to a temperature change, a temperature measuring arrangement for determining the temperature of the liquid film, the temperature measurement arrangement being capable of producing a signal, and a control and evaluation device for controlling one of the heating arrangement and the cooling arrangement and the temperature measuring arrangement, the method comprising subjecting the portion of the liquid film to a temperature change using one of the heating and the cooling arrangement, measuring the temperature of the portion using the temperature measuring arrangement, assigning the value which corresponds to the thickness of the liquid film to the temperature change using the evaluation device, and producing a signal related to the value.